Process for preparing coated synthetic fibers from normally crystalline polymers



PROCESS FOR PREPARING COATED SYNTHETIC FHBERS FROM N ORMALLY CRYSTALLINE POLY- MERS .lohn R. Frost, Midland, Mich., assignor to The Dow (Ihemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed May 28, 1956, Ser. No. 587,450

5 Claims. (Cl. 18--54) This invention relates to an improved process for preparing oriented rough surfaced synthetic fibers from normally crystalline polymers. More particularly it relates to an improved process for fusing such fibers.

It is known that synthetic fibers and other continuous filamentary articles may be prepared from normally crystalline polymers by extrusion, by wet or dry spinning of a spinning dope, or by the continuous coagulation of a latex of the polymer. In both wet spinning and the latex coagulation methods a serious problem in drying and fusing or sintering of the fibers results. Usually the fibers must be dried before sintering so as not to entrap moisture or solvent within the core of the fiber which would result in bubbles or voids during sintering. The dried fibers become tacky during the sintering steps, and, when it is attempted to sinter a tow of several fibers, considerable fiber to fiber bonding or sticks occur. Those sticks are commercially useless and must be removed from the tow by costly procedures. Attempts have been made to prevent fiber to fiber contact during the sintering operation. Those procedures were difficult to carry out, slowed production, and were not completely successful in preventing breaks.

Another problem encountered in the synthetic fiber art is the high degree of sheen imparted by the smooth 9 unobstructed surface of the fibers. That smooth surface also causes a necessity for imparting to such fibers an artificial crimp to minimize their slippage past one another in yarn making and weaving operations. It has been proposed to alleviate those difiiculties by causing the surface of the fibers to be roughened either mechanically or by a scaly coating and to approach thereby the hand, appearance, and texture of wool. Although such roughening has largely been successful, the technique has been limited to an extra procedure following the preparation of the smooth-surfaced, non-tacky fibers.

In view of the above difiiculties encountered in the preparation of synthetic fibers it would be desirable to have and it is the principal object of this invention to provide an improved process for simultaneously sintering a tow of fibers prepared from normally crystalline polymers.

It is a further object to provide such a process whereby fiber to fiber bonding during sintering is eliminated.

It is a still further object to provide such a process for producing synthetic fibers having wool-like characteristics.

Other objects will be apparent as the description proceeds.

The above and related objects are accomplished by means of a process whereby a tow consisting of a plurality of unoriented unsintered continuous synthetic fibers of a normally crystalline polymer are coated with a dispersion of a coating material having a softening temperature higher than the sintering temperature of the synthetic fiber and then subjected to a temperature known to cause sintering of the synthetic fibers, super-cooling the tow of synthetic fibers, and stretching the tow as fully as possible without rupture of the fibers.

The normally crystalline polymers are well known in the art. Typical examples of such polymers include the copolymers of vinylidene chloride with another mono- 3,62%,fi8l Patented Mar. 6, 1962 ethylenically unsaturated monomer and wherein the vinylidene chloride is present in predominant amount.

Methods for preparing fibers by either wet spinning or latex coagulation are well-known. In a typical wet spinning procedure a solution of polymer is expressed through a spinneret into a coagulant or precipitant to form a loosely bonded filament coagulum having very little strength. The filamentary coagulum is then desolvated, dried, sintered, and oriented sequentially to produce a useful synthetic fiber.

In preparing fibers by the coagulation of a latex, a stream of latex or a stream of coagulant is spun into a bath of coagulant or latex respectively and the so-formed continuous loosely-bonded filamentary coagulum removed from the bath at approximately the same rate at which it is formed. The filamentary coagulum is then washed, dried, sintered, and oriented to produce a useful synthetic fiber.

The coating materials useful in this process, and capable of forming a continuous sheath about the unsintered filamentary coagulum, are those having a softening temperature that is higher than the sintering temperature of the polymers forming the unsintered coagulum, and having less ultimate elongation than the sintered fiber. Typical of such materials are dispersions of polyamides, emulsions of high melting waxes, and latexes of polymers and copolymers. Many such dispersions, emulsions, and la texes are available commercially and one having the required properties can be selected readily. Especially useful coating materials are the monoongano hydrogen polysiloxanes or mixtures or copolymers of monoorgano hydrogen and diorganopolysiloxanes. As preferred materials for use in this invention may be mentioned methyl hydrogen polysiloxane, mixtures consisting of at least 25 percent by weight of methyl hydrogen polysiloxane with not more than percent by weight of dimethyl polysiloxane, and

copolymers of methyl hydrogen and dimethyl polysiloxanes. These materials are available commercially in latex form from which they are film forming under the action of catalysts such as the usual driers. Preferred catalysts for use with the methyl derivatives are the metallic salts of aliphatic carboxylic acids.

In operation the process consists of thoroughly wetting the tow of dried unfused fibers in the dispersion of filmforming coating material followed by drying to form the continuous sheath of coating material about the fiber. It is desirable that this drying occur first at a temperature below the sintering temperature of the fiber to insure the formation of the non-tacky sheath before sintering the fibers. The tow of coated fibers is then subjected to a temperature capable of sintering the fibers, but below the softening temperature of the coating material forming the sheath, until the fibers are sintered. The tow of fibers is then super-cooled and stretched as fully as possible without rupture to orient the individual fibers. The stretching process fractures the relatively inelastic sheath into a multitude of tiny irregularly shaped scales. The scales are then separated from each other by the extension of the fiber, leaving a central fiber having a scaly rough coating adhered thereto. Such fibers are wool-like in appearance and hand.

The advantages and operation of the process of this invention will be more apparent from the following illustrative example wherein all parts and percentages are by Weight unless otherwise indicated.

Example A tow of fibers was prepared by spinning a latex of a polymer composed of 97 percent vinylidene chloride and 3 percent acrylonitrile and having 40 percent non-volatile solids into an aqueous coagulant of calcium chloride.

The filamentary articles so produced were continuously removed, washed, and dried. The tow of filamentary articles was then immersed at room temperature in a bath consisting of 5 parts by volume of an 18 percent solids emulsion of a mixture of methyl hydrogen polysiloxane and dimethyl polysiloxane, 1 part by volume of zinc-2- ethylhexoate emulsion, and 5 parts by volume of water. The tow was thoroughly wet in about 1 minute after which it was air dried for about 30 minutes until a continuous sheath about the core of polymer was formed. The tow was next held in a radiant heating zone at 170 C. for a few seconds until the fibers changed from opaque white to translucent, indicating completion of fusion. The tow was then cooled and stretched as fully as possible without rupture of the individual fibers. At no time during this process was any fiber to fiber bonding noticed. The fibers had a multitude of tiny irregularly shaped scales on the surface giving the fibers a non-lustrous appearance and a warm hand.

When the process was repeated using a percent solids emulsion of a mixture of methyl hydrogen polysiloxane and dimethyl polysiloxane with zinc-2-ethyl hexoate, in the bath some fiber to fiber bonding occurred because at the solids concentration employed a, continuous sheath was not formed.

By way of contrast when the process was again repeated but without the coating step, the tow had considerable fiber to fiber bonding during the fusion step and no useful fibers were obtained.

1 claim:

1. In a process for preparing a tow of synthetic fibers from normally crystalline vinylidene chloride polymers by spinning said polymers from a coagulable medium through a plurality of orifices into a bath of coagulant, washing and drying the so-formed tow of fibrous coagula, sintering the fibrous coagula of said tow, and finally stretching said tow as fully as possible without rupture to produce orientation therein, the improvement consisting.

of coating said tow after drying and prior to sintering with a coating material capable of 'forming a continuous sheath about said fiber, having a softening temperature above the sintering temperature of said fibers, and having less elongation of the temperature of orientation than said fibers, air drying said coating material to form a continuous, relatively inelastic sheath about each individual fiber comprising said tow, subjecting the tow of sheathed fibers to a temperature above the sintering temperature of said fibers but below the softening temperature of said sheath until sintering of said fibers is complete, cooling said tow, and finally stretching said tow as fully as possible without rupture of said fibers to cause orientation in said fibers and to fracture said sheath into tiny scales adhering to said fibers.

2. The improved process claimed in claim 1 wherein said normally crystalline polymer consists of a copolymer of vinylidene chloride with another monoethylenically unsaturated monomer and wherein the vinylidene chloride is present in predominant amount.

3. The improved process claimed in claim 1 wherein said coating material comprises an organo hydrogen polysiloxane.

4. The improved process claimed in claim 3 wherein said organo hydrogen polysiloxane is methyl hydrogen polysiloxane.

5. The improved process claimed in claim 3 wherein said coating material consists of at least 25 percent by weight of a methyl hydrogen polysiloxane and correspondingly not more than percent by weight of a dimethyl polysiloxane.

References Cited in the file of this patent UNITED STATES PATENTS 2,238,694- Graves Apr. 15, 1941 2,572,936 Kulp Oct. 30, 1951 2,588,365 Dennett Mar. 11, 1952 2,588,367 Dennett Mar. 11, 1952 2,695,835 Hare Nov. 30, 1954 2,732,318 Keil Jan. 24, 1956 2,736,946 Stanton et a1. Mar. 6, 1956 2,737,456 Le Boeuf Mar. 6, 1956 

1. IN A PROCESS FOR PREPARING A TOW OF SYNTHETIC FIBERS FROM NORMALLY CRYSTALLINE VINYLIDENE CHLORIDE POLYMERS BY SPINNING SAID POLYMERS FROM A COAGULABLE MEDIUM THROUGH A PLURALITY OF ORIFICES INTO A BATH OF COAGULANT, WASHING AND DRYING THE SO-FORMED TOW OF FIBROUS COAGULA, SINTERING THE FIBROUS COAGULA OF SAID TOW, AND FINALLY STRETCHING SAID TOW AS FULLY AS POSSIBLE WITHOUT RUPTURE TO PRODUCE ORIENTATION THEREIN, THE IMPROVEMENT CONSISTING OF COATING SAID TOW AFTER DRYING AND PRIOR TO SINTERING WITH A COATING MATERIAL CAPABLE OF FORMING A CONTINUOUS SHEATH ABOUT SAID FIBER, HAVING A SOFTENING TEMPERATURE ABOVE THE SINTERING TEMPERATURE OF SAID FIBERS, AND HAVING LESS ELONGATION OF THE TEMPERATURE OF ORIENTATION THAN SAID FIBERS, AIR DRYING SAID COATING MATERIAL TO FORM A CONTINUOUS, RELATIVELY INELASTIC SHEATH ABOUT EACH INDIVIDUAL FIBER COMPRISING SAID TOW, SUBJECTING THE TOW OF SHEATHED FIBERS TO A TEMPERATURE ABOVE THE SINTERING TEMPERATURE OF SAID FIBERS BUT BELOW THE SOFTENING TEMPERATURE OF SAID SHEATH UNTIL SINTERING OF SAID FIBERS IS COMPLETE, COOLING SAID TOW, AND FINALLY STRETCHING SAID TOW AS FULLY AS POSSIBLE WITHOUT REPTURE OF SAID FIBERS TO CAUSE ORIENTATION IN SAID FIBERS AND TO FRACTURE SAID SHEATH INTO TINY SCALES ADHERING TO SAID FIBERS. 